The present invention relates to a method for the in-situ formation of reinforcing members in an elastomeric matrix and an elastomeric matrix made thereby.
Those skilled in the art have long understood that the addition of reinforcing materials to an elastomer greatly improves the strength properties of an elastomeric matrix. Difficulties sometimes arise, however, in the mixing of the reinforcing material into the elastomer. Polyaromatic amide fibers, for example (such as Kevlar.RTM., available from E. I. Dupont Nemours Inc., Wilmington, Del.), are not easily mixed with an elastomer and have a tendency to form "rats' nests" in the mix. Because of this, such fibers are prepared in a masterbatch, which requires four or five passes in a mixer, and in production the masterbatch is mixed with about four times its weight in rubber, which requires another four or five passes in the mixer.
Although the degree of difficulty encountered in mixing some other types of fibers and reinforcing materials into an elastomer is not as great as that encountered for Kevlar, in all cases the mixing procedure is time and labor intensive and represents a considerable portion of the expense of a reinforced elastomeric article.
Part of the difficulty encountered in mixing prior art reinforcing materials into an elastomer relates to the size of the materials. Kevlar, and similar fibers, generally have a length of 0.1 mm to 3 mm and an aspect ratio of 50 to 100. Such fibers are known in the art as macro fibers. Also because of their size, such fibers may detract from the appearance of articles when close to the surface of the article. Because of strength anomalies, large fibers may not be suitable for use in articles which are made having small dimensions and low gauges, and because of their size may be observable in finely defined areas of large articles.
It is known in the art that micro fibers (0.1 micron to 1000 microns in length, with an aspect ratio of 10 to 1000) can be formed in-situ in a polymer matrix. Isayev et al., for example in U.S. Pat. No. 4,728,698 teach the in-situ formation of fibers in a polymer matrix by the addition of a liquid crystal polymer to a base polymer followed by mixing and extrusion.
It is an object of the present invention to include reinforcing materials into an elastomeric matrix substantially in one step, reducing the time and labor needed to provide reinforcement for an elastomeric article. It is also an object of the present invention to control the size and orientation of fiber type reinforcements in such articles whereby such reinforcement can be used in articles having small dimensions and low gauges, and in finely defined areas of large articles.